Molecular detection and quantitation can be carried out with various methods depending on the type of the molecule. For instance, nucleotide sequences can be detected by virtue of their sequence complementarily to a probe or primer, or in fewer occasions with a protein that recognize the sequence. A protein is commonly detected with an antibody that specifically recognizes and binds the protein, as in enzyme-linked immunosorbent assay (ELISA) or Western Blot assay. Molecular detection methods and systems have broad applications, in particular clinically, for detection that can give a disease diagnosis, for instance.
Detecting small molecules, for example mono- and disaccharides, or larger molecules, like proteins that are shielded with glycosylation, presents a challenge. Unlike nucleic acids, they do not have a complementary sequence, and unlike proteins, they lack a unique targetable sequence. Thus, their structures makes it difficult to generate highly-specific, high-affinity antibodies to detect their presence.
Diol compounds alone, below a certain size threshold, are undetectable with a nanopore, as exemplified by Calin Plesa, Stefan W. Kowalczyk, Ruben Zinsmeester, Alexander Y. Grosberg, Yitzhak Rabin, and Cees Dekker. “Fast translocation of proteins through solid state nanopores.” Nano letters 13, no. 2 (2013): 658-663. Moreover, even those diol-containing molecules that are detectable may not be distinguishable. A diol compound will yield the same nanopore signature as all other molecules of comparable size/charge, preventing discrimination.
What is needed therefore, is a fast and inexpensive method of detecting, distinguishing and quantifying small molecules and metabolites, or larger proteins with small molecule post translational modifications. These biomolecules may serve as biomarkers for the presence of disease.